Hydraulic materials give cured products excellent in properties such as strength and durability, and therefore have been widely used in cement compositions such as cement paste, mortar, and concrete. Such hydraulic materials are indispensable for the construction of civil engineering and constructional structures. The hydraulic materials after being cured incur dispersion of an unaltered water component remaining therein owing to an atmospheric temperature and humidity, and suffer drying shrinkage probably caused thereby. This causes the generation of cracks in the cured products, leading to a reduction in the strength and the durability. When the strength or durability of the civil engineering and building structures is reduced, serious problems occur such as decline of safety and increased cost for repair.
In order to solve such problems, the importance of shrinkage reducing agents for a hydraulic material that suppress the development of drying shrinkage in cured products of hydraulic materials has been acknowledged, and the technical innovation thereof has been actively developed.
The following compounds are disclosed, for example, as conventional shrinkage reducing agents: a copolymer containing a structural unit derived from an unsaturated carboxylic acid monomer and a structural unit derived from an ethylenically unsaturated monomer containing an oxyalkylene group at a side chain (see Patent literature documents 1 to 3); and a graft polymer obtained by graft polymerization of an ethylenically unsaturated monomer to a polyether compound having a structure in which one oxyalkylene chain is bonded to a residue of a compound containing one active hydrogen atom (see Patent literature documents 4 and 5).